This invention relates to a computer system containing a storage system, and more particularly, to a differential copy setting method.
In a computer system in general where a plurality of host computers are run, one storage system is shared by the host computers to be run in a centralized manner, thereby reducing the running and management cost of the storage system. In the centralized storage system, input from and output to (I/O) the servers (host computers) concentrate in a single disk drive, and redundant array of inexpensive disks (RAID) is employed as a technology of speeding up I/O. RAID achieves quick I/O by grouping together a plurality of physical disks that are to be managed as one disk (parity group) and allowing the grouped physical disks to operate in parallel with one another. A computer system of this type usually partitions a parity group into a plurality of storage areas. The storage areas are referred to as “logical volumes” here.
A computer system can lose data through a breakdown of its storage system due to a disaster, a physical failure due to, for example, the expiration of the service life of a disk, data destruction by a computer virus, an operational mistake made by a user, and the like. Computer systems generally prepare for such data loss by backing up data periodically and using the backup data for restoration.
Storage systems that are attracting attention lately are ones having a function of copying data from a logical volume that is being used for business operation (primary volume) to another logical volume (secondary volume). This function enables a computer system to back up data stored in a logical volume without stopping the daily business operation. The pair consisting of the primary volume and the secondary volume is a “copy pair”. Information indicating which logical volume is paired with which logical volume to form a copy pair is “copy pair configuration information”. The relation between the secondary volume and a parity group to which the secondary volume belongs is a “parity group relevant to the copy pair”.
A storage system as the one described above has a copy function with which data is backed up by copying every piece of data in the primary volume to the secondary volume after the volumes are paired as a copy pair, thereby making data in the primary volume and data in the secondary volume consistent (synchronized) with each other. After the synchronization, the business operation is started and the storage system merely records updated places where data is newly written in the primary volume, instead of executing copy between the primary volume and the secondary volume. When it is time to take a backup, data in the updated places alone is copied from the primary volume to the secondary volume based on the record of updated places. The storage system thus accomplishes fast backup (see, for example, JP 2001-331378 A). The data in the updated places to be copied is a “differential”. Copying the differential data from the primary volume to the secondary volume is “differential copy”.
The characteristics of a logical volume vary depending on the type of physical disks constituting its parity group (for example, disks coupled by fibre channel or disks coupled by serial advanced technology attachment (ATA)) and the RAID type (e.g., RAID level 1 or RAID level 2). It is therefore desirable to pair a primary volume with a secondary volume whose characteristics fit the primary volume as a copy pair.
Running a storage system in a centralized manner increases the count of logical volumes per storage system. This means that there are that much more logical volumes to choose from for the secondary volume of a backup-purpose copy pair, and makes it difficult to determine which logical volume as a secondary volume fits the primary volume.
As a technology of alleviating this problem, a method has been disclosed in which the computer system manages a table recording the characteristics of each logical volume to present appropriate secondary volume candidates to the user on the basis of the correlation between the characteristics of the primary volume and the characteristics of an unused logical volume (see JP 2005-18185 A, for example). This enables the user to choose a secondary volume that fits the primary volume from many logical volumes with ease.
Or the sophisticated storage system described above is equipped with other various functions. An example of those functions is related to relocation of data between physical disks within the storage system. With this function, the association of a logical volume that stores the data and that has been associated with the pre-relocation allocated place in a physical disk is switched to the post-relocation allocated place in a physical disk (see JP 2000-293317 A, for example). The data relocation is referred to as “data migration” here.
Generally speaking, a storage system backs up data periodically. When differential copy is started as part of data backup processing, backup data that has been stored in the secondary volume is destroyed by overwriting and can no longer be used. Data in the secondary volume cannot be used as new backup data, either, because it is incomplete until the differential copy is finished. In short, there is substantially no backup data in the secondary volume during differential copy. Data loss is therefore a possibility if a failure occurs in the primary volume during differential copy.
Also, requests to read data out of the primary volume which are issued during differential copy in order to extract a differential affect the business operation. In these and other various respects, it is desirable to keep differential copy processing time within a given period of time.
A storage system shared by a plurality of host computers prepares a copy pair for each host computer. In the case where the secondary volumes of the respective copy pairs belong to the same parity group, executing differential copy in the copy pairs at the same time causes the concentration of load on this parity group and accordingly prolongs the differential copy processing time.
This problem cannot be solved by the technology described in JP 2005-18185 A where candidates for the secondary volume are presented based only on the characteristics of a logical volume.